The present invention is in the field of devices and apparatus for fluid sensing, fluid filtering, and fluid catalysis.
This invention relates to devices and methods for sensing, filtering, and catalyzing fluids. More specifically, this invention relates to oxidized metallic foils useful in such devices and methods, particularly in the automotive industry.
Recent changes in transportation regulations call for the on-board diagnosis of the performance of vehicle emissions systems. These regulations call for devices that alert a driver when the exhaust system of the driver""s car is not functioning properly. Among species to be monitored are carbon monoxide (CO), hydrocarbons, and nitrogen oxides. A challenge exists to monitor the above and other species over the life of a vehicle, in a way that can survive extreme temperatures and the presence of water.
Many ceramics have found use in fluid-sensing applications, whether the fluid is a liquid or gas. For example, titania-based thick films have been demonstrated to be effective sensors of CO gas in auto and industrial emissions. Semiconducting TiO2xe2x88x92x can undergo surface reactions with a reducing gas species, such as CO, that lead to changes in resistivity proportional to the concentration of such gas species. In order to provide a large effective surface area for such reactions (i.e., for a relatively high sensitivity and rapid response), a resistance-based, titania gas sensor usually takes the form of a thin film or porous, fine-grained pellet. The ultimate success of a ceramic, however, will depend on the ability to prepare the ceramic with an appropriate pore size and structure, and maximizing the surface area of the ceramic that is capable of contacting a fluid.
It is thus an object of the present invention to develop a simple, durable, freestanding porous ceramic device capable of determining changes in concentration of select chemical species within a fluid, and similar devices to filter the fluid or catalyze a reaction with the fluid whereby any chemical species may be captured or altered by the device. It is also an object to develop methods of using such devices.
Although described with respect to the field of ceramic-based fluid sensors and the like, it will be appreciated that similar advantages may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes free-standing, shaped ceramic-bearing bodies useful in fluid sensors and fluid-sensing devices. The fluids may be either liquids or gases. The shaped ceramic-bearing bodies of the present invention are also useful as fluid filters and in fluid filtering devices. The shaped ceramic-bearing bodies may also be used as catalysts for reactions in contacting fluids. The present invention also includes machines and instruments using those aspects of the present invention. The invention additionally includes methods and processes for using such ceramic-bearing bodies. The methods and processes of the present invention may be applied using procedures and protocols known and used in the arts to which they pertain.
In broadest terms, the present invention includes a ceramic-based fluid sensor for sensing the change in concentration of a species in a fluid in contact therewith, comprising (1) a ceramic-bearing body fabricated from a shaped, metal-bearing precursor, the ceramic-bearing body comprising at least one ceramic phase having an open pore structure; and (2) at least two electrodes in electrical contact with the ceramic-bearing body; whereby the ceramic-bearing body is capable of undergoing a change in electrical behavior in response to a change in concentration of a species in the fluid. The ceramic-based fluid sensor may additionally have a fluid conduit in communication with the ceramic-bearing body, whereby the change in concentration of a species in the fluid passing through the fluid conduit changes the electrical behavior of the ceramic-bearing body. The change in electrical behavior, such as a change in resistivity or capacitance, may arise in changes at an interface between phases while the sensor is in contact with the fluid.
The shape of the sensor may be any predetermined shape and may be adapted to fit within the space of the fluid conduit. The predetermined shape of the ceramic-bearing sensor may be arrived at prior to oxidation of the metal-bearing precursor. The determination of appropriate shape may take into account the malleability and porosity of the metal-bearing precursor body. The metal-bearing precursor body may be shaped by any appropriate means, such as by rolling, extrusion or forging the metal-bearing precursor body into the predetermined shape or by bending a metal-bearing precursor foil over an appropriately-shaped rigid form. After oxidation, the resultant ceramic-bearing body may have substantially the same shape as the metal precursor prior to oxidation. The ceramic-bearing body may comprise a shaped, oxidized metallic foil. The metal-bearing precursor foil may be of any appropriate material, such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, cerium, molybdnum, manganese, ruthenium, tin, thorium, uranium and tungsten or any combination thereof. The ceramic-bearing body may be doped with any appropriate element, such as a transition metal. The ceramic portions of the ceramic-bearing body may comprise separate layers of the body. The spacing of these layers may be controlled during the fabrication and use of the body by monitoring and appropriately modifying the surrounding conditions. The electrodes may be comprised of any appropriate material and form, such as copper, silver or gold contacts, leads wire or paste. The ceramic phase, or one of the ceramic phases, may be produced by the reaction of at least one of the aforementioned metals within the shaped precursor with one species of a fluid. The fluid species may be an atom, ion, or molecule comprised of one or more elements selected from the group consisting of oxygen, nitrogen, carbon, hydrogen, chlorine, sulfur, and combinations thereof.
Also included in the present invention is, in broadest terms, a fluid sensing device for sensing the change in concentration of a species in a fluid in contact therewith comprising: (1) a shaped, oxidized metallic foil comprising at least one ceramic phase having an open pore structure, the oxidized metallic foil containing a dopant element; (2) at least two electrodes in electrical contact with the oxidized metallic foil; and (3) a fluid conduit in communication with the oxidized metal-bearing precursor foil; whereby the doped oxidized metallic foil is capable of undergoing a change in electrical behavior in response to a change in concentration of a species in the fluid passing through the fluid conduit. The metallic foil may be of any appropriate element, such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, cerium, molybdnum, manganese, ruthenium, tin, thorium, uranium and tungsten or any combination thereof. The ceramic may be doped with any appropriate dopant element as detailed above. The electrodes may be comprised of any appropriate material and form, such as copper leads, silver contacts, or gold paste. The ceramic phase, or one of the ceramic phases, may be produced by the reaction of at least one of the aforementioned metals within the shaped foil with one species of a fluid. The fluid conduit may be of any appropriate type, such as an automotive exhaust pipe, a factory smokestack, or a chemical drainpipe. The change in electrical behavior may be any detectable change, such as a change in resistivity, conductivity, or capacitance. The device measuring such change may be any appropriate device, such as an ampmeter, oscilloscope, or voltmeter.
The present invention also includes, in broadest terms, a titanium-oxide based fluid sensor for sensing the change in concentration of carbon monoxide in a fluid in contact therewith, comprising: (1) a doped titanium-oxide foil fabricated from a shaped, copper-doped titanium-bearing precursor, the foil comprising at least one ceramic phase having an open pore structure; and (2) at least two electrodes in electrical contact with the foil, such as contacts comprised of gold paste painted on the foil, whereby the doped titanium-oxide foil is capable of undergoing a change in resistivity in response to a change in concentration of carbon monoxide in the fluid. The fluid sensor may additionally have a fluid conduit in communication with the foil, whereby a change in concentration of carbon monoxide in the fluid passing through the fluid conduit affects a change in resistivity of the foil. The predetermined shape of the sensor may be such that the sensor is adapted to fit within the space of the fluid conduit.
Also included in the present invention is, in broadest terms, a fluid sensing device for sensing the change in concentration of carbon monoxide in a fluid in contact therewith comprising: (1) a shaped, titanium-oxide foil comprising at least one ceramic phase having an open pore structure, the titanium-oxide foil containing a copper dopant; (2) at least two electrodes in electrical contact with the titanium-oxide foil; and (3) a fluid conduit in communication with the titanium-oxide foil; whereby the doped titanium-oxide foil is capable of undergoing a change in resistivity in response to a change in concentration of carbon monoxide in the fluid passing through the fluid conduit. The electrodes may be comprised of any appropriate material and form, such as copper leads, silver contacts, or gold paste.
The present invention also includes, in broadest terms, a method of sensing a change in concentration of a species in a fluid, the method comprising the steps of: (1) obtaining an shaped ceramic-bearing body comprising at least one ceramic phase having an open pore structure; (2) bringing the shaped ceramic-bearing body into contact with the fluid, the fluid being capable of altering the electrical behavior of the shaped ceramic-bearing body; and (3) measuring the resultant change in the electrical behavior of said shaped ceramic-bearing body. The change in electrical behavior may relate to an alterance of any applicable, measurable characteristic, such as resistance, conductivity, or capacitance.
Also included in the present invention is, in broadest terms, a ceramic-based catalysis device for catalyzing a reaction of a species in a fluid in contact therewith comprising a ceramic-bearing body fabricated from a shaped, metal-bearing precursor, the ceramic-bearing body comprising at least one ceramic phase having an open pore structure whereby the ceramic-bearing body is capable of catalyzing a reaction in the fluid. The device may additionally have a fluid conduit in communication with the ceramic-bearing body, whereby fluid passing through the conduit undergoes a reaction catalyzed by the ceramic-bearing body. The ceramic-bearing body may be of any appropriate material listed previously, such as an oxidized metallic foil. The ceramic-bearing body may be doped with any appropriate element, such as a dopant metal selected from the group consisting of transition metals.
The present invention also includes, in broadest terms, a method of fluid catalysis comprising the steps of: (1) obtaining a shaped ceramic-bearing body comprising at least one ceramic phase having an open pore structure; and (2) bringing the shaped ceramic-bearing body into contact with a fluid, the fluid comprising at least one species capable of undergoing a reaction catalyzed by the ceramic-bearing body. The species of fluid may be any appropriate species capable of having a reaction catalyzed by a ceramic of a type described previously, such as CO or H2.
Also included in the present invention is, in broadest terms, a ceramic-based fluid filter for removing at least one species of a fluid in contact therewith comprising a ceramic-bearing body fabricated from a shaped, metal-bearing precursor, the ceramic-bearing body comprising at least one ceramic phase having an open pore structure whereby the ceramic-bearing body is capable of entraining at least one species of the fluid. The filter may also have a fluid conduit in communication with the ceramic-bearing body, whereby at least one of the species of the fluid becomes entrained in the ceramic. The ceramic-bearing body may be of any appropriate material listed previously, such as an oxidized metallic foil. The ceramic-bearing body may be doped with an appropriate element, such as a dopant metal selected from the group consisting of transition metals.
Also included in the present invention is, in broadest terms, a ceramic-based fluid filter for removing at least one type of particulate from a fluid in contact therewith comprising a ceramic-bearing body fabricated from a shaped, metal-bearing precursor, the ceramic-bearing body comprising at least one ceramic phase having an open pore structure whereby the ceramic-bearing body is capable of entraining at least one type of particulate contained in the fluid. The ceramic-bearing body may entrain the particulates by either having an appropriate pore size such that the particulates become entrained in the pores, or by an electrical charge developed on the surface of the ceramic-bearing body whereby particulates may be attracted to and adhere to the surface of the ceramic-bearing body. The charge may be generated by any appropriate means, as through the accumulation of a surface static charge or through an appropriate applied voltage. The filter may also have a fluid conduit in communication with the ceramic-bearing body, whereby at least one type of solid particulate contained in the fluid becomes entrained in the ceramic-bearing body. The ceramic-bearing body may be of any appropriate material listed previously, such as an oxidized metallic foil. The ceramic-bearing body may be doped with an appropriate element, such as a dopant metal selected from the group consisting of transition metals.
The present invention also includes, in broadest terms, a method of filtering a fluid containing multiple species, the method comprising the steps of: (1) obtaining a shaped ceramic-bearing body fabricated from a shaped, metal-bearing precursor, the appropriate ceramic-bearing body comprising at least one ceramic phase having an open pore structure; and (2) bringing the shaped ceramic-bearing body into contact with the fluid, at least one of the multiple species capable of becoming entrained in the ceramic-bearing body. The species to be filtered by the fluid may be any appropriate species capable of being entrained in a ceramic-bearing body of any type described previously.